Explain how to connect GDB.

Change-Id: Ibb374491a5445d183d3b22ece926d7d18d56e568
diff --git a/kvm-unit-tests/run_test.sh b/kvm-unit-tests/run_test.sh
index a696d20..6372b49 100755
--- a/kvm-unit-tests/run_test.sh
+++ b/kvm-unit-tests/run_test.sh
@@ -129,6 +129,8 @@
 	if [ -z "${TIMEOUT}" ]; then
 		TIMEOUT=0s
 	fi
+	>&2 echo "Test will wait for GDB connection. Connect with"
+	>&2 echo "$ build/aarch64/run_gdb.sh -e gdb-multiarch"
 fi
 
 # If not otherwise specified, use default timeout value.